532 
ALBAN STEWART 
years. The largest one in the collection has a cross-diameter of 6 cm. 
while the apparently normal stem just above it has a similar diameter 
of 1.6 cm. This portion of the stem has eight annual rings of growth, 
while the gall has but one ring of growth next to the pith which is 
normal, the rest of them being greatly altered in their structure. 
The second ring of growth from the pith shows less alteration than 
does the woody tissue outside of it. Its outer boundary is plainly 
marked, and, so far as one can judge by examination with a hand lens, 
it differs structurally from a normal ring of growth in having greater 
width and broader rays. The tissue outside of this shows no indica- 
tion of annual rings except just inside the cambium where such a ring 
is differentiated in places. Another smaller gall examined has a 
diameter of 3.4 cm. and two apparently normal rings of growth at 
the center, while the stem just above it has a diameter of 8 mm. and 
five rings of growth. The tree from which the galls were taken has 
been infested with them for many years according to the inhabitants 
of the region. Similar galls are caused by this insect on Quercus 
coccinea, Q. ilicifolia, Q. nigra, and Q. rubra according to Cook (5, p. 28). 
It is rather difficulc to locate galls of this kind in their earliest stages 
as there is usually no external evidence of them beyond a slight 
swelling of the bark^ such as might result from other causes. A cross 
section of an early stage is shown in fig. i. The bark is about twice 
as thick on the side where the gall is located as it is on the opposite 
side of the stem, but there is practically no increase in the thickness 
of the wood. Apparently the first effect of the gall stimulus is to 
cause the formation of a larger amount of bark tissue than normal. 
Outside of the increase in the thickness of the bark no other striking 
abnormalicies appear in the neighborhood of the gall. 
The larval chamber is not as well defined as it is in later stages of 
development. The cavity containing the larva is irregular, con- 
forming roughly in shape to it. The protecting layer of stone cells, 
somewhat lightly colored in fig. i, is semilunar in outline and is only 
developed on the outside of the chamber in the section shown. Higher 
up in the same series of sections, however, a complete ring of stone 
cells has been formed. Just below the cavity, shown in fig. i, there is 
a radial segment of brown-colored parenchyma cells which extends 
from the base of the cavity to a slight depression in the cork layers 
covering the gall on the outside. This segment is surrounded by 
1 The term bark is used to include all tissues located outside the cambium. 
